Sensing Element For Respirator

ABSTRACT

A sensing element includes a substrate including an electrically non-conductive surface, at least one high surface energy region, and an electrode pair structure disposed on the electrically non-conductive surface. The electrode pair structure includes at least one pair of electrodes having a gap therebetween. At least one of the electrodes is at least partially within the at least one high surface energy region. The sensing element is configured to sense fluid-soluble particulate matter.

BACKGROUND

Particulate matter (PM) sensors are sensing elements that are configuredto enable quantification of the concentration of solid particles in anenvironment, most commonly an environment where particles are suspendedin a gas phase. PM sensors have received an increase in attention overthe last decade as a result of increased awareness of the possibleimpact of PM on human health. PM sensors are commonly used to enableenvironmental PM monitoring, diesel engine soot particle output, andparticle filter efficiency measurements, including respirator fittesting. Most of the sensor systems fall into one of the followingcategories: 1) mass based measurements, which monitor the mass ofparticles deposited over time by use of a mass balance or quartz crystalmicrobalance (typically used in environmental monitoring), 2) opticalbased measurements, where an optical signal is used to monitor theconcentration of particles in an airstream (typically used inenvironmental monitoring and quantitative respirator fit testing), and3) electrical conductivity sensing, where the deposition of electricallyconductive particles on a pair of electrodes results in a measurableelectrical signal (typically used in diesel engine soot monitoring,because soot particles are electrically conductive).

Mass based measurements are generally cumbersome, or require relativelyexpensive quartz crystal elements and frequency counting electronics.Optical sensing also requires relatively expensive optical systems andhigh-power requirements. Electrical property sensors can be madeinexpensively, because in their most simplistic form can consist only ofa pair of electrodes on a substrate. However, existing PM sensors basedon electrical property measurements, such as those employed in dieselengine soot sensing, require that the particles of interest beconductive in their solid state. This requirement precludes the sensorsfrom being used to monitor solid particles which are electricallyinsulating, such as solid salt particles. Additionally, electricalproperty sensors can be affected by changes in environmental conditions,such as temperature and humidity changes.

SUMMARY

The present disclosure relates to a sensing element of a respirator. Inparticular, this disclosure relates to an electronic sensing elementconfigured to undergo a change in an electrical property (resistance,capacitance, or other AC impedance properties) in the presence of afluid ionizable aerosol. The electronic sensing element may beconfigured to enable compensation of background noise induced byenvironmental factors, for example, temperature, humidity, and gaseouscomponent interactions.

In one aspect, a sensing element includes a substrate including anelectrically non-conductive surface, at least one high surface energyregion, and an electrode pair structure disposed on the electricallynon-conductive surface. The electrode pair structure includes at leastone pair of electrodes having a gap therebetween. At least one of theelectrodes is at least partially within the at least one high surfaceenergy region. The sensing element is configured to sense fluid-solubleor fluid-ionizable particulate matter.

The above summary is not intended to describe each embodiment or everyimplementation of the present disclosure. A more complete understandingwill become apparent and appreciated by referring to the followingdetailed description and claims taken in conjunction with theaccompanying drawings. In other words, these and various other featuresand advantages will be apparent from a reading of the following detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of top, front and side view of anillustrative sensing element.

FIG. 2 are schematic diagrams of top views of two illustrative sensingelements.

FIG. 3 is a schematic diagram cross-sectional view of an illustrativesensing element.

FIG. 4A is a schematic diagram of top, front and side view of anotherillustrative sensing element.

FIG. 4B is a schematic diagram of top, front and side view of anotherillustrative sensing element.

FIG. 5A is a flow diagram of an illustrative method of making a sensingelement.

FIG. 5B is a flow diagram of another illustrative method of making asensing element.

FIG. 6 is a schematic diagram cross-sectional view of the sensingelement of FIG. 4A illustrating fluid disposed on the electrode pairstructures.

FIG. 7 is a schematic diagram cross-sectional view of an illustrativesensing element with a filtering element.

FIG. 8 is a schematic diagram cross-sectional view of the sensingelement of FIG. 7 illustrating fluid disposed on the electrode pairstructures.

FIG. 9 is a schematic diagram of top view of another illustrativesensing element.

FIG. 10 is a schematic diagram of top view of another illustrativesensing element.

FIG. 11 are graphs illustrating the sensor response to differentconcentrations of NaCl in water, the top three graphs illustrate theresistance (solid lines) and reactance (dashed lines), as a function offrequency, measured by the sensor when coated with a liquid layer of thesolution indicated. The bottom three graphs illustrate the impedancemagnitude (solid lines) and phase shift (dashed lines), as a function offrequency, measured by the sensor when coated with a liquid layer of thesolution indicated. Z=impedance magnitude, Theta=phase shift,R=resistance, and X=reactance.

FIG. 12A-12C are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for different surface modification andcoating systems applied to salt aerosol sensor.

FIG. 13A-13D are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for O2+TMS plasma+zwitterionic silanefollowed by different coat weights of glucose applied to salt aerosolsensor.

FIG. 14A-14C are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for sensors with and without a filterelement.

FIG. 15 is a schematic diagram of an illustrative respirator sensorsystem.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which are shown byway of illustration several specific embodiments. It is to be understoodthat other embodiments are contemplated and may be made withoutdeparting from the scope or spirit of the present disclosure. Thefollowing detailed description, therefore, is not to be taken in alimiting sense.

All scientific and technical terms used herein have meanings commonlyused in the art unless otherwise specified. The definitions providedherein are to facilitate understanding of certain terms used frequentlyherein and are not meant to limit the scope of the present disclosure.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the properties sought tobe obtained by those skilled in the art utilizing the teachingsdisclosed herein.

The recitation of numerical ranges by endpoints includes all numberssubsumed within that range (e.g. 1 to 5 includes 1, 1.5, 2, 2.75, 3,3.80, 4, and 5) and any range within that range.

As used in this specification and the appended claims, the singularforms “a”, “an”, and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise.

As used in this specification and the appended claims, the term “or” isgenerally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

As used herein, “have”, “having”, “include”, “including”, “comprise”,“comprising” or the like are used in their open-ended sense, andgenerally mean “including, but not limited to”. It will be understoodthat “consisting essentially of”, “consisting of”, and the like aresubsumed in “comprising,” and the like.

As used herein, the terms “fluid-soluble” and “fluid-ionizable” areequivalent in this disclosure.

The present disclosure relates to a sensing element of a respirator. Inparticular, this disclosure relates to an electronic sensing elementconfigured to undergo a change in an electrical property (resistance,capacitance, or AC impedance) in the presence of a fluid ionizableaerosol. The electronic sensing element may be configured to enablecompensation of background noise induced by environmental factors, forexample, temperature, humidity, and gaseous component interactions. Theelectronic sensing element may also be configured to be easily pluggedinto and removed from a sensor to enable readout of the sensing elementsignal. In some cases, the sensor may be wireless, enabling a completelywireless aerosol monitoring system, with disposable sensor elements,that may be configured to be integrated with a respiratory protectiondevice. The electronic sensing element may enable the electricaldetection of some particles which are non-conducting in the solidparticle state, and also provides a means of background compensation forenvironmental changes. The electronic sensing element is configured todetect particles which dissolve into conductive components in a fluid.For example, crystalline salt particles, such as sodium chlorideparticles, are electrically insulating in the solid particle state, butdissolve into conductive sodium and chloride ions in polar fluids, suchas water. The sensing element enables detection of these particlesbecause the surface of the sensing element is designed such that a fluidfilm forms in the region between the electrodes. When the particles ofinterest impact the sensing element, they dissolve into the fluid, whichthen enables detection. The sensing element may be designed such thatthe fluid film forms from gases in the environment. As an example, thefluid may be formed by the condensation of water vapor from humanbreath. In this example, the sensing element may be placed inside of arespirator for use in respirator fit testing. Aerosolized salt particleswhich leak into the respirator may impact the sensing element surface,which has a fluid layer formed by the water vapor in the exhaled breathof the wearer, to enable leak detection of the respirator.

Background compensation may be provided by a second pair of electrodeson the sensing element surface (although the two pairs of electrodes mayshare a single common ground element). This second pair of electrodes,the reference electrodes, may have a particle filtering element abovethe surface of the electrode which may prevent the particles of interestfrom interacting with the reference electrode. However, with appropriatepressure drop of the filtering element, the same gaseous componentswhich interact with the first pair of electrodes may be able to passthrough the filter and also interact with the second pair of referenceelectrodes. The surface modification surrounding the electrode pairs maybe patterned such that there is a discontinuity in the fluid between theelectrode pairs. This discontinuity may prevent the migration ofelements from one electrode pair to the other. This assembly results ina reference electrode pair which experiences the environmental effectsexperienced by the first electrode pair, but a lesser amount of theparticulate effects. This enables a way of removing the environmentaleffects from the signal recorded by the first pair of electrodes. Insome embodiments, the reference electrode pair may have the particulatematerial of interest predisposed on the surface, such that thebackground compensation signal includes the environmental interactionwith the PM of interest. For example, if the sensing element isconfigured to monitor sodium chloride particles, the reference pair maybe pre-loaded with a known amount of sodium chloride, so that when thesignal from the first pair of electrodes matches the signal from thereference pair, it can be inferred that the first pair of electrodes hasthe same quantity of sodium chloride as the reference pair. While thepresent disclosure is not so limited, an appreciation of various aspectsof the disclosure will be gained through a discussion of the examplesprovided below.

FIG. 1 is a schematic diagram of top, front and side view of anillustrative sensing element 10. The sensing element 10 is configured tointeract with an environment of interest. The sensing element 10includes a substrate 1 having an electrically non-conductive surface 11,at least one high surface energy region 3, and an electrode pairstructure 2 disposed on the electrically non-conductive surface 11. Theelectrode pair structure 2 includes at least one pair of electrodes A, Bhaving a gap 12 therebetween. At least one of the electrodes A or B isat least partially within the at least one high surface energy region 3.The sensing element 10 is configured to sense fluid-soluble particulatematter.

At least some of the high surface energy region 3 may be overlapping andadjacent to the electrode pair structure 2 or the electrode pair A, B,and may be configured to interact with an environment of interest, by,for example, promoting the condensation of gaseous molecules orparticulate matter into a condensed fluid on the high surface energyregion 3 and particularly within the gap 12 of the electrode pairstructure 2 or the electrode pair A, B, or promoting the sensitivity toa component of interest.

Fluid-soluble particulate matter is particulate matter that may, or maynot, be electrically conductive in the solid-state form, but may ionizeinto electrically conductive components in a fluid, such as water.Dissolution of the fluid-soluble particulate matter in the fluid mayprovide a change in an electrical property of the liquid that may bedetected or sensed by the electrode pair structure 2. One usefulfluid-soluble particulate matter is sodium chloride (NaCl).

The electrodes A and B in the at least one pair of electrodes A, B maybe co-planar with respect to each other. The electrodes A and B in theat least one pair of electrodes A, B may be parallel extending orinterdigitated, or have any other useful configuration. The gap 12defined by a distance between the electrodes A and B in the at least onepair of electrodes A, B may have a lateral distance G_(L) value of anyuseful value. This lateral distance G_(L) value may be in a range from25 to 125 micrometers. The electrodes may have any useful lateral widthE_(L) value. This lateral width E_(L) value may be in a range from 25 to125 micrometers. The electrodes A and B may be formed of anyelectrically conducting and corrosion or oxidation resistant materialsuch as various metals or metal alloys.

The high surface energy region 3 may be patterned onto the substrate 1or electrically non-conductive surface 11 to provide for selectivedeposition of liquid onto the substrate 1 or electrically non-conductivesurface 11 for contacting the electrode pair structure 2. The highsurface energy region 3 may be at least partially, or completelysurrounded or circumscribed by one or more low surface energy regions 6.The high surface energy region 3 may provide for selective deposition ofliquid or water to form a liquid layer or liquid volume within the gap12 of the electrode pair structure 2 onto the high surface energy region3. Thus, the liquid layer or liquid volume may contact both electrodes Aand B in the electrode pair structure 2. The high surface energy region3 may define any useful shape or surface area.

The phrase “high surface energy region” refers to a surface region thatexhibits an advancing water contact angle of less than 90 degrees, orless than 80 degrees, or less than 60 degrees, and/or preferably lessthan 45 degrees, as measured per ASTM D7334-08. It is noted that a watervolume of 20 microliters, which is a general recommendation in ASTMD7334-08, may be too large for proper testing depending on the surfacegeometry. It is necessary that the water volume is small enough inrelation to the size of the surface region such that the advancingcontact angle is not disturbed by the confinement of the region.

The phrase “low surface energy region” refers to a region with lowersurface energy than the high surface energy region, such that the lowsurface energy region has an advancing water contact angle that isgreater than that of the high surface energy region. The low surfaceenergy region may have an advancing water contact angle that is 1-10degrees, or 10-20 degrees, or 20-45 degrees, and/or preferably more than45 degrees, greater than that of the high surface energy region.

For example, the high surface energy region 3 may have an advancingwater contact angle of 20 degrees, and the low surface energy region 6may have an advancing water contact angle of 60 degrees. In anotherexample, the high surface energy region 3 may have an advancing watercontact angle of 70 degrees, and the low surface energy region 6 mayhave an advancing water contact angle of 100 degrees. The difference inadvancing water contact angles promotes confinement of a condensed fluidto the predefined regions, which may minimize undesirable interactions.The advancing water contact angle may be impacted by the hydrophilicnature of the surface region, or the hygroscopic nature of materials inthe surface region which effectively alter the advancing water contactangle.

The high surface energy region 3 may be formed by surface treatment ofthe substrate 1 or electrically non-conductive surface 11. These surfacetreatments include, for example, plasma, chemical modification, and thelike. Plasma treatments may include oxygen plasma treatment. Chemicaltreatment includes deposition or vapor deposition of silanes orsiloxanes to form, for example, a siloxane surface or a zwitterionicsiloxane surface defining the high surface energy region 3. Chemicaltreatment may also, or alternatively, include deposition of hygroscopicmaterials to define the high surface energy region 3. The high surfaceenergy region 3 may have a dissolvable ion content of less than 1E-9moles/mm². For example, a 1 mm² surface region with 10 ng of sodiumchloride has a dissolvable ion content of approximately 3.45E-10moles/mm² (1.72E-10 moles/mm² contributed by sodium and 1.72E-10moles/mm² contributed by chloride) due to the potential dissociation ofthe sodium chloride into sodium and chloride ions when water condenseson the region. The dissolvable ion content impacts the surfaceresistivity of the sensor. However, the surface resistivity is alsoimpacted by the ambient environment, such as the relative humidity, dueto the varied interactions of the high surface energy region 3 with theenvironment. For example, for the case of a 1 mm² surface region with 10ng of sodium chloride, the surface resistivity will be large in lowhumidity environments in which the sodium chloride remains a crystallinesolid, and the surface resistivity will be lower in high humidityenvironments in which the sodium chloride absorbs moisture from the airand dissolves into a liquid solution. The dissolvable ion content isalso impacted by the ionic dissociation constant of the species in thehigh surface energy region. For example, sodium chloride has a largeionic dissociation constant in water, while the ionic dissociationconstant of a compound such as glucose is much lower. As a result, foran equivalent molar amount of glucose loaded on a surface, thedissolvable ion content of the glucose surface will be significantlylower than that of a surface with sodium chloride.

Hygroscopic materials include materials which absorb or adsorb waterfrom the surrounding environment, and preferably those which absorb oradsorb water vapor from the surrounding gaseous medium. For example, thehygroscopic material may be a salt, an acid, a base, or preferably acompound with a low ionic dissociation constant in water such as awater-absorbing polymer, a monosaccharide, a polysaccharide, an alcohol,or more preferably a polyol, such that the surface resistivity change ofthe sensor due to absorption or adsorption of water is minimized.

The polyol may be a polymeric polyol or a monomeric polyol and maypreferably be a sugar alcohol, such as sorbitol. The hygroscopic layeris preferably a compound which enhances water retention and may also bewithin the class of compounds known as humectants. The hygroscopicmaterial is preferably a material which has a deliquescence point ofless than 100 percent relative humidity, or less than 90 percentrelative humidity, or more preferably less than 80 percent relativehumidity at 25 degrees Celsius and 1 atmosphere of pressure. Thedeliquescence point is taken to refer to the relative humidity at whichthe material absorbs enough water from the surrounding gaseous mediumsuch that it dissolves and forms a liquid solution. The formation of theliquid solution may enhance the performance of the fluid ionizableparticulate matter sensing element by providing a liquid solution that aparticle may dissolve into. The hygroscopic material and coating weightare preferably chosen such that the electronic mobility of the ions ofthe dissolved particulate matter of interest is minimally decreased bythe effects of the hygroscopic material.

The substrate 1 may be formed of any electrically non-conductivematerial. The substrate 1 may be a laminate or a single materialconstruction. The substrate 1 may be formed of any material used ascircuit board or electrical sensor substrates. The substrate 1 may beformed of any glass or dielectric resin. Illustrative substrate 1material is commercially available from Advanced Circuits, Colorado,USA, among other printed circuit board fabrication entities.

FIG. 2 are schematic diagrams of top views of illustrative sensingelements 10. The sensing element 10 includes a substrate 1 comprising anelectrically non-conductive surface 11, at least one high surface energyregion 3, and an electrode pair structure 2 disposed on the electricallynon-conductive surface 11, as described above. The electrode pairstructure 2 includes at least one pair of electrodes A, B having a gap12 therebetween. At least one of the electrodes A or B is at leastpartially within the at least one high surface energy region 3, asdescribed above. The sensing element 10 is configured to sensefluid-soluble particulate matter.

FIG. 2 on the left illustrates an interdigitated electrode pair A, Bhaving two opposing pairs of interdigitated members A₂ and B₂. The gap12 between interdigitated members A₂ and B₂ may have a lateral distancevalue of any useful value. This distance value may be in a range from 25to 125 micrometers. The interdigitated members A₂ and B₂ may have anyuseful lateral width. This lateral width may be in a range from 25 to125 micrometers. The interdigitated members A₂ and B₂ may have anyuseful length such as a range from 500 to 10,000 micrometers. Theinterdigitated members A₂ and B₂ may be formed of any electricallyconducting and corrosion or oxidation resistant material such as variousmetals or metal alloys. The interdigitated electrode pair A, B is shownwith four interdigitated members however the interdigitated electrodepair A, B may have any number of total interdigitated members, such asin a range from 2 to 50, or 4 to 40.

FIG. 2 on the right illustrates another embodiment of the sensingelement 10 where the electrode pair structure 2 defines a firstelectrode B at least partially surrounding a second electrode A anddefining a gap 12 therebetween.

FIG. 3 is a schematic diagram cross-sectional view of one illustrativesensing element 10. FIG. 3 provides an illustration of a suitablelayering structure that can be applied to the electricallynon-conductive surface 11 and electrode pair structure 2 to define thehigh surface energy region 3 and enhance the electrical impedanceresponse to a fluid soluble target particulate material such as a saltaerosol, for example. The electrode pair structure 2 includes at leastone pair of electrodes A, B having a gap 12 therebetween.

An illustrative surface treatment layer 120 may include a zwitterionicsilane layer or surface chemically grafted to a siloxane layer orsurface (where the siloxane surface may be formed by anoxygen+tetramethyl silane plasma treatment as illustrated in FIG. 5A).This illustrative surface treatment layer 120 may be referred to as asilane surface treatment layer 120. This illustrative surface treatmentlayer 120 may exist predominantly on the surface of the electricallynon-conductive surface 11 in between electrode pair structure 2 orbetween at least one pair of electrodes A, B or within the gap 12. Theillustrative surface treatment layer 120 may define the high surfaceenergy region 3.

FIG. 5A is a flow diagram of a process for forming the illustrativesurface treatment layer 120. This process includes forming electrodes A,B on the electrically non-conductive surface 11 at step 210. Then amasking layer is applied to define the high surface energy region on theelectrically non-conductive surface 11 at step 220, such that at leastone electrode A or B is at least partially within the defined highsurface energy region. The masking layer may be applied to theelectrically non-conductive surface 11, such that some region of theelectrically non-conductive surface 11 is exposed to the subsequenttreatments, and some regions are protected from the subsequenttreatments. The regions protected from subsequent treatments may formlow surface energy regions. A suitable masking layer is any layer thatforms a desired pattern for forming the desired surface composition andmay resist plasma treatment in defined locations. For example, asuitable masking layer is a tape commercially available under the tradedesignation “3M Vinyl Tape 491” from 3M, MN, USA.

The masked article is placed in a vacuum chamber at step 230. The vacuumchamber may provide a vacuum environment of 100 mTorr or less, or 50mTorr or less. Then an oxygen plasma is applied to the masked article atstep 231. Oxygen gas (for example, at a concentration of 500 parts permillion (ppm)) may be introduced and formed into a plasma in fluidcontact with at least some of the electrode surface for a period of time(for example, sixty seconds). In certain embodiments, the plasma may begenerated by applying a 500 W radiofrequency field. Then a silane isdeposited or vapor deposited onto the plasma treated article at step232. Tetramethyl silane (for example, at a concentration of 150 ppm) maythen be added to the plasma for a period of time (for example, thirtyseconds). The tetramethylsilane flow may be interrupted, and oxygenplasma continues for a period of time (for example, sixty seconds). Thesecond oxygen plasma is applied to the masked article at step 233. Thenthe plasma treated article is removed from the vacuum chamber at step234.

Then a zwitterionic silane solution is coated onto the treated articleat step 240. The solution containing a zwitterionic silane, for exampleat 2 wt % in water, is applied in fluid contact with the sensing elementsurface for a period of time (for example, ten seconds). The coatedarticle is blown dry at step 241 and then baked at an elevatedtemperature for a period of time (for example, ten minutes at 110° C.).The sensing element 10 is then rinsed at step 250 with deionized waterand dried at step 251.

The silane surface treatment layer 120 may be formed of compounds havingformula (I) as described in International Patent Publication No.WO2016/044082A1 (Riddle, et al.):

(R¹O)_(p)—Si(Q¹)_(q)-W—N⁺(R₂)(R₃)—(CH₂)_(m)-Z^(t−)  (I)

wherein:

each R¹ is independently a hydrogen, methyl group, or ethyl group;

each Q¹ is independently selected from hydroxyl, alkyl groups containingfrom 1 to 4 carbon atoms, and alkoxy groups containing from 1 to 4carbon atoms;

each R² and R³ is independently a saturated or unsaturated, straightchain, branched, or cyclic organic group (preferably having 20 carbonsor less), which may be joined together, optionally with atoms of thegroup W, to form a ring;

W is an organic linking group;

Z^(t−) is —SO₃ ⁻, —CO₂ ⁻, —OPO₃ ²⁻, —PO₃ ²⁻, —OP(═O)(R)O⁻, or acombination thereof, wherein t is 1 or 2, and R is an aliphatic,aromatic, branched, linear, cyclic, or heterocyclic group (preferablyhaving 20 carbons or less, more preferably R is aliphatic having 20carbons or less, and even more preferably R is methyl, ethyl, propyl, orbutyl);

p is an integer of 1 to 3;

m is an integer of 1 to 11;

q is 0 or 1; and

p+q=3.

Suitable examples of zwitterionic silane compounds of Formula (I) aredescribed in U.S. Pat. No. 5,936,703 (Miyazaki et al.), including, forexample:

(CH₃O)₃Si—CH₂CH₂CH₂—N⁺(CH₃)₂—CH₂CH₂CH₂—SO³⁻; and

CH₃CH₂O)₂Si(CH₃)—CH₂CH₂CH₂—N⁺(CH₃)₂—CH₂CH₂CH₂—SO3⁻.

Other examples of suitable zwitterionic silane compounds and theirpreparation are described in U.S. patent application Ser. No. 13/806,056(Gustafson et al.), including, for example:

In some embodiments, a layer of salt material 140 is applied to thesensing element 10 or surface treatment layer 120 of the sensing element10. The layer of salt material 140 may provide for a referenceelectrical property value of the electrode pair A, B. This may be usefulwhen two or more electrode pairs are utilized with the sensing element10. The layer of salt material 140 may be disposed on the high surfaceenergy region 3.

In some embodiments, a layer 130 comprising a hygroscopic material maybe applied to the sensing element 10 or surface treatment layer 120 ofthe sensing element 10, and then allowed to dry. In some of theseembodiments, a layer of salt material 140 may be disposed on or with thehygroscopic material layer 130 within the high surface energy region 3of the sensing element 10. The salt material 140 may mix with thehygroscopic material layer 130 to form a combined hygroscopic materialand salt layer 130, 140.

In some embodiments, a hygroscopic material layer 130 is disposed on thesensing element 10 and is in contact with at least one of layers 11, 120and electrode pair structure 2. FIG. 5B is a flow diagram of the processof FIG. 5A described above with the addition of the hygroscopic materiallayer 130. The sensing element 10 with the surface treatment layer 120of FIG. 5A is then treated with a hygroscopic material solution (forexample, a hygroscopic material solution may be 0.1 wt % sorbitol inwater) at step 260 and heated to 110 degrees Celsius at step 261. Thisillustrative hygroscopic material layer 130 may exist predominantly onthe surface of the electrically non-conductive surface 11 in betweenelectrode pair structure 2 or between at least one pair of electrodes A,B or within the gap 12 or on the surface treatment layer 120. Theillustrative surface treatment layer 130 may define the high surfaceenergy region 3.

In some embodiments, the addition of a hygroscopic material layer 130may be used to modify the hygroscopic properties of a sensing element 10surface to which it is applied and may define the high surface energyregion 3 on the sensing element 10. When used on a surface of a sensingelement 10 that functions based on electrical impedance variations, somehygroscopic materials have the property of altering hygroscopicproperties without contributing mobile ions in solution. Additionally,some hygroscopic materials have another advantageous property of lowvapor pressure. The hygroscopic properties of polyols are due to theirwater activity, which is influenced by presence of a large number ofhydroxyl groups in the molecule. The water activity thermodynamics of avariety of polyol sugar alcohols are described by Compernolle, S. andMuller, J.-F., Atmos. Chem. Phys., 14, 12815-12837 (2014). For example,sorbitol is shown to form a thermodynamically stable water-sorbitolmixture at relative humidity greater than 40%. This property may beadvantageous when the sensing element 10 to be modified functions basedon the ionization of particles in a liquid. The presence of ahygroscopic material, such as a sugar alcohol, on the sensing element 10or surface of the electrically non-conductive surface 11 in betweenelectrode pair structure 2 or between at least one pair of electrodes A,B or within the gap 12 or on the surface treatment layer 120 may enableuse in a wider range of humidity environments.

In certain embodiments, the hygroscopic material layer 130 includescompounds with a plurality of hydroxyl groups. For example, thehygroscopic material layer 130 may be comprised of polyethylene glycolavailable from Sigma-Aldrich, MO, USA. In other suitable examples, thepolyol layer may include at least one sugar alcohol. Some examples ofsuitable sugar alcohols include glycerol, erythritol, arabitol, xylitol,ribitol, mannitol, sorbitol, galactitol, allitol, iditol, maltitol,isomalitol, lactitol, dulcitol, and talito, all available fromSigma-Aldrich, MO, USA. In other suitable examples, the polyol layer 130may include saccharide compounds. Some examples of suitable saccharidesinclude glucose, fructose, galactose, sucrose, lactose, cellulose andstarch available from Sigma-Aldrich, MO, USA.

The thickness of the surface treatment layer 120 or the silane surfacetreatment layer 120 may be any useful thickness. In many embodiments,the surface treatment layer 120 or the silane surface treatment layer120 is less than 50 nanometers, or from 1 to 50 nanometers thick.

When present, the thickness of the hygroscopic material layer 130 may beany useful thickness. In some embodiments, the thickness of thehygroscopic material layer 130 may be from 0.1 to 10 micrometers thick.Thicknesses greater than 10 micrometers or less than 0.1 micrometers maybe useful also. The thickness of the hygroscopic material layer 130 mayimpact the total amount of water absorption, as well as the kinetics ofabsorption. By altering the thickness, which may be accomplished byaltering the coating weight, the sensing element response may beimproved for a given environment. Examples of the impact of thehygroscopic layer thickness is illustrated in FIG. 13A-13D.

The sensing element 10 may omit one or more of the layers describedabove, and the layers may be constructed with a range of coating weightsand thickness combinations, as desired. When used with a sensing element10 that functions based on electrical impedance variations, the silanesurface treatment layer 120 has the property of altering surfaceproperties without contributing significant amounts of mobile ions insolution. In some embodiments, the addition of a hygroscopic materiallayer 130 may be used to modify the hygroscopic properties of sensingelement 10 and assist in defining the high surface energy region 3 onthe sensing element 10. When used with a sensing element 10 thatfunctions based on electrical impedance variations, the hygroscopicmaterial layer 130 may have the property of altering surface propertieswithout contributing significant amounts of mobile ions in solution.

FIG. 4A is a schematic diagram of top, front, and side view of anotherillustrative sensing element 10 having two electrode pair structures 2,4, or two pairs of electrodes A, B and C, D.

The sensing element 10 is configured to interact with an environment ofinterest. The sensing element 10 includes a substrate 1 including anelectrically non-conductive surface 11, two high surface energy regions3, and two electrode pair structures 2, 4 disposed on the electricallynon-conductive surface 11. Each electrode pair structure 2, 4 includesat least one pair of electrodes A, B and C, D having a gap 12 _(AB) and12 _(CD) therebetween. At least a portion of each electrode pairstructure 2, 4 is within the corresponding high surface energy region 3.The high surface energy region 3 may be discontinuous, such that a lowersurface energy region 6 separates the high surface energy region 3corresponding to each electrode pair A, B and C, D, as illustrated. Thesensing element 10 is configured to sense fluid-soluble orfluid-ionizable particulate matter. A low surface energy region 6 mayseparate the two high surface energy regions 3. A conductive region 5may electrically connect the electrode pair structure 2, 4 with sensingelectronics. This electrode configuration may be referred to asincluding four electrodes A, B, C, and D where two pairs of electrodesare formed A-B and C-D.

The low surface energy region 6 may assist in keeping liquid in each ofthe two high surface energy regions 3 separate from each other. Regionsoutside of the perimeter of the high surface energy regions 3 may have alower surface energy than the surface energy within the perimeter of thehigh surface energy regions 3. Thus, liquid vapor or water vapor mayselectively condense and form a liquid layer or liquid volume thatremain within the perimeter of the high surface energy regions 3.

Water vapor may be produced by human breath inside of a respirator, suchas a filtering facepiece respirator (FFR) or elastomeric respirator, forexample. This water vapor may condense onto the high surface energyregion 3 of the sensing element. In an example, salt aerosol particles,such as sodium chloride, may come into contact with this condensed watervapor so that the salt particle dissolves and alters an electricalproperty (for example, impedance) of at least one of the electrode pairsA, B and C, D. The spatially separated surface treatments enabledistinctly separate signals by preventing molecular migration betweenthe electrode pair structures 2 and 4.

In some embodiments, at least a portion of a region surrounding at leastone of the electrode pair structures 2, 4 may have a particulate or saltmaterial predisposed on the electrode pair structures 2, 4 or within thegap 12 _(AB), 12 _(CD) therebetween (as illustrated in FIG. 3). Forexample, sodium chloride may be predisposed on a surface surrounding anelectrode pair structure 2 or 4 or within the gap 12 _(AB) or 12 _(CD)to generate an electrical impedance related to the quantity ofpredisposed sodium chloride. This may be referred to as a referenceelectrode. The solid material (sodium chloride, for example) may bedisposed or provided within the perimeter of one high surface energyregion 3 in a known amount. Once water vapor condenses on this highsurface energy region 3 the known amount of solid material (sodiumchloride, for example) is dissolved and may provide a referenceelectrical property or reference electrode (electrode pair structure 2or 4) that a sensing electrode (remaining electrode of 2 or 4) may becompared to during testing or the sensing operation.

FIG. 4B is a schematic diagram of top, front, and side view of anotherillustrative sensing element 10.

The sensing element 10 is configured to interact with an environment ofinterest. The sensing element 10 includes a substrate 1 comprising anelectrically non-conductive surface 11, two high surface energy regions3, and two electrode pair structures 2, 4 disposed on the electricallynon-conductive surface 11. Each electrode pair structure 2, 4 includesone electrode and share a common electrode C and having a gap 12 _(AC),12 _(BC) therebetween. At least a portion of each electrode pairstructure 2, 4 is within the corresponding high surface energy region 3.The sensing element 10 is configured to sense fluid-soluble particulatematter. A low surface energy region 6 may separate the two high surfaceenergy regions 3. A conductive region 5 may electrically connect theelectrode pair structure 2, 4 with sensing electronics. This electrodeconfiguration may be referred to as comprising three electrodes A, B,and C where two pairs of electrodes are formed A-C and B-C and whereelectrode C is common to both electrode pairs.

The sensing element may be configured to be electrically coupled ordecoupled to one or more additional electronic elements by a physicalproximity to one or more electronic elements. In some embodiments, forexample, an electrically conducting region 5 may be configured forphysical contact with an electronic element in a connector. In someembodiments, for example, an electrically conducting region 5 may beconfigured to electrically couple with another electronic elementwithout physical contact via a time-varying electromagnetic field.

FIG. 6 is a schematic diagram cross-sectional view of the sensingelement 10 of FIG. 4A illustrating fluid 9 disposed on the electrodepair structures 2, 4. The sensing element 10 includes a substrate 1including an electrically non-conductive surface 11, two high surfaceenergy regions 3, and two electrode pair structures 2, 4 disposed on theelectrically non-conductive surface 11. Each electrode pair structure 2,4 includes at least one pair of electrodes A, B, and C, D having a gap12 _(AB) and 12 _(CD) therebetween. At least a portion of each electrodepair structure 2, 4 is within the corresponding high surface energyregion 3. The sensing element 10 is configured to sense fluid-solubleparticulate matter. A low surface energy region 6 may separate the twohigh surface energy regions 3. The configuration of the high surfaceenergy regions 3 enables the selective condensation of water or liquidvapor onto these high surface energy regions 3 to form the liquidbubbles, or liquid layers, or liquid volumes 9.

In embodiments with multiple electrode pairs A, B, and C, D, the regionsof different surface energies may be configured such that fluid 9, asillustrated in an example in FIG. 6, preferentially wets the highsurface energy regions 3 surrounding at least one of the electrode pairsA, B, or C, D, but the fluid 9 does not make fluid contact with theother electrode pair A, B, or C, D. The preferential separation of fluidcontact with the different electrode pairs is shown in FIG. 6, wherefluid 9 preferentially wets the regions proximal to the two electrodepair structures 2 and 4, but does not form a fluid bridge between thepairs A, B, and C, D, due to the low surface energy region 6. Liquid orwater 9 has a lower affinity to wet region 6, producing multipledistinct fluid regions 9 that are not in fluid communication with oneanother.

FIG. 7 is a schematic diagram cross-sectional view of an illustrativesensing element 10 with a filtering element 7. FIG. 8 is a schematicdiagram cross-sectional view of the sensing element of FIG. 7illustrating fluid 9 disposed on the electrode pair structures 2, 4.

The filtering element 7 may be configured such that it prevents at leastsome particles or a component from the environment from contacting atleast one electrode pair C, D. In some embodiments, the particulatefilter 7 may be a nonwoven filter element. In some embodiments, astandoff material 8 is disposed on the electrically non-conductivesurface 11, such that the material 8 surrounds at least a portion of anelectrode pair structure 4, and the filter material 7 is disposed on thestandoff material 8 such that the filter material 7 is configured to notphysically contact the electrode pair C, D.

One suitable example of a standoff material 8 is an adhesive foamcommercially available under the trade designation “3M Urethane FoamTape 4056” from 3M Co., MN, USA, for example. The standoff material 8 orfoam may have an ionic content of less than 1000 ppm, such that theextraction of ions by a condensed fluid is minimized. As an example,this configuration may result in a reference electrode pair C, D, thatmay interact with gaseous compounds in the environment which are able topass through the filter material 7. However, at least some particles areintercepted by the filter material 7 and are prevented from interactingwith the reference electrode pair C, D.

The filtering element 7 may provide the only airflow communication withthe electrode pair structure 4 or electrode pair C, D and thesurrounding environment, but does not provide particulate communicationwith the electrode and the surrounding environment. Thus, the electrodepair structure 4 may operate as a real-time reference electrode that mayremove environmental effects from the sensing signal of the sensingelectrode pair structure 2 or electrode pair A, B (not protected by thefiltering element 7), for example. In other embodiments, a fixed amountof solid material of interest, such as salt 140 (see FIG. 3) or sodiumchloride, may be disposed on the reference electrode pair structure 4 orelectrode pair C, D and contained by the filtering element 7. Thisconfiguration may provide a reference electrode pair or electrode pairstructure 4 or electrode pair C, D that has a set signal to the sensingelectronics for comparison with the sensing electrode pair or structure2 or electrode pair A, B (not protected by the filtering element 7).

FIG. 9 is a schematic diagram of the top view of another illustrativesensing element 10. The sensing element 10 includes a substrate 1comprising an electrically non-conductive surface 11, two high surfaceenergy regions 3, and two electrode pair structures 2, 4 disposed on theelectrically non-conductive surface 11. Each electrode pair structure 2,4 includes at least one pair of electrodes A, B and C, D having a gap 12_(AB) and 12 _(CD) therebetween. At least a portion of each electrodepair structure 2, 4 is within the corresponding high surface energyregion 3. The sensing element 10 is configured to sense fluid-solubleparticulate matter. A low surface energy region 6 may separate the twohigh surface energy regions 3. Here one electrode pair A, B is betweenthe other electrode pair C, D. The inner electrode pair C, D is shown aslinear, parallel and co-extending, however, the inner electrode pair C,D may be interdigitated as described above.

FIG. 10 is a schematic diagram of the top view of another illustrativesensing element 10. The sensing element 10 includes a substrate 1comprising an electrically non-conductive surface 11, one high surfaceenergy region 3, and one electrode pair structure 2 disposed on theelectrically non-conductive surface 11. The electrode pair structure 2includes at least one pair of electrodes A, B having a gap 12therebetween. At least a portion of each electrode pair structure 2 iswithin the high surface energy region 3. The sensing element 10 isconfigured to sense fluid-soluble particulate matter. A low surfaceenergy region 6 may surround or circumscribe the high surface energyregion 3. The electrode pair A, B is shown as linear, parallel andco-extending, however, the electrode pair A, B may be interdigitated asdescribed above. One or more perforations, holes, or apertures 15 extendthrough the substrate 1. The perforations, holes, or apertures 15 mayprovide for air flow communication through the sensing element 10 andmay improve particle contact with the sensing element 10 or improve thefluid dynamics of the fluid near the electrode pair A, B.

A protective film or removable liner (not shown) may be removablyadhered to the sensing element 10 to provide protection during transportand installation of the sensing element 10 and electrode pair structures2, 4. The sensing element 10 may be applied to a respirator or personalprotective device or element, as described below.

FIG. 15 is a schematic diagram of an illustrative respirator sensorsystem 300. The system 300 includes a respirator 310, a sensor 320including a sensing element (as described herein), and a reader 330configured to be in wireless communication with the sensor 320. Thesensor 320 is positioned substantially into an interior gas space of therespirator 310.

The respirator sensor system 300 may be configured to detect thepresence of unfiltered air within the interior gas space of therespirator 310. The respirator sensor system 300 may be configured todetect the leakage of unfiltered air within the interior gas space ofthe respirator 310.

As described above, the sensing element is configured to sensefluid-soluble particulate matter when a liquid layer is disposed in agap on at least a part of the surface of the sensing element. Fluidionizable particles may at least partially dissolve and may at leastpartially ionize in the liquid layer, resulting in a change in anelectrical property between at least two of the electrodes.

Water vapor may be produced by human breath inside of the respirator andcondense onto the high surface energy region of the sensing element andform the liquid layer. In an example, salt aerosol particles, such assodium chloride, may come into contact with this condensed water vaporso that the salt particle dissolves and alters an electrical property(for example, impedance) of at least one of the electrode pairs. Thischange in electrical property may be sensed by the sensor 320 andwirelessly communicated to a remote reader 330. The transport of thefluid ionizable particulate matter to the sensing element may beaffected by human breath.

The sensing element is a fluid ionizable detection element that may beconfigured such that the condensing vapor does not condense uniformly onthe surface of the sensing element, as described above. The fluidionizable detection element may be further configured such that thecondensed vapor in contact with at least one electrode does not form acontinuous condensed phase to at least one other electrode.

The respirator 310 may be any personal protective respirator articlesuch as a filtering facepiece respirator or elastomeric respirator, forexample. The sensor 320 may include a power source, communicationinterface, sensing electronics, and antenna. The sensor 320 power sourcemay be a battery, a rechargeable battery, or energy harvester.

The sensing element may be configured to be replaceable and mechanicallyseparable from the sensor 320. The sensing element may be in removablecommunication with the sensor 320. The sensor 320 may be reusable byreplacing a used or spent sensing element with a fresh or new sensingelement.

The sensor 320 may be fixed to, or adhered to, or connected to aninterior surface of the respirator 310 or personal protective device orelement. The interior surface may define a interior gas space of therespirator once the respirator 310 or personal protective device orelement is worn by a user. The interior gas space is in airflowcommunication with the breath of the user wearing the respirator 310 orpersonal protective device or element. The sensor 320 may be removablypositioned or attached within the interior gas space. The sensor 320 maybe removably positioned or attached to the interior surface of therespirator 310.

The sensor 320 may be fixed to, or adhered to, or connected to aninterior surface of the respirator 310 by any useful attachment system,such as, adhesive, hook and loop or suction, for example. The sensorattachment system may not penetrate the thickness of the interiorsurface of the respirator 310, the sensor attachment system may notextend through the thickness of the interior surface of the respirator310, the sensor attachment system may not be in contact with an exteriorsurface of the respirator 310. The sensor attachment system may notpenetrate a surface of the respirator in contact with an exterior gasspace.

The size and weight of the sensor 320 are selected such that the sensordoes not interfere with a wearer's use of the respirator 310. The sizeof the sensor 320 and a weight of the sensor 320 are selected such thatthe sensor 320 does not alter the fit the respirator 310 on a wearer.The sensor 320 may have a weight in a range from 0.1 to 225 grams,preferably less than 10 grams, or from 1 to 10 grams. A sensor weighing225 grams may not alter the fit of the respirator if the respirator issufficiently tight, but lower weights are preferred so as to reduce theweight of the respirator. The sensor 320 may have a volume in a rangefrom 0.1 to 50 cm³, preferably less than 10 cm³, or from 1 to 10 cm³.

The sensor 320 may wirelessly communicate with a remote reader 330. Thesensor 320 may wirelessly communicate data to the reader 330 regardingchanges in an electrical property of the sensing element. Thecommunication between the reader 330 and the sensor 320 is viaelectromagnetic communication, such as via magnetic field, or Near FieldCommunication, or Bluetooth Low Energy, or optical illumination anddetection, WiFi, Zigbee, or the like.

The sensor 320 may and reader 330 may communicate with one another aboutone or more constituents of a gas or aerosol within the interior gasspace. The sensor 320 may and reader 330 may communicate with oneanother about physical properties related to a gas within the interiorgas space, such as temperature, pressure, humidity, and the like. Thesensor 320 may and reader 330 may communicate with one another aboutparameters used to assess physiological conditions of a wearer of therespirator.

The reader 330 may include a power source, communication interface,control electronics, and antenna. The reader 330 may wirelesslycommunicate with a remote device 350 via the internet 340. The reader330 may communicate with the internet 340 via wireless connection. Thereader 330 may communicate with the internet 340 via direct wiredcommunication. The remote device 350 may include any of memory, datastorage, control software, or at least one processor to receive andutilize the data or information provided by the reader 330 directly orvia the internet 340.

The respirator sensor system 300 may be utilized to detect fluidionizable particles in a gaseous medium. The method includes contactinga gaseous medium with a fluid ionizable particulate matter sensingelement, and condensing a component of the gaseous medium on at least aportion of the fluid ionizable particulate matter sensing element; anddetermining an electrical property at a first point in time between apair of electrodes of the fluid ionizable particulate matter detectionelement; and determining an electrical property at a second point intime between a pair of electrodes of the fluid ionizable particulatematter detection element; and determining a value related to thepresence of fluid ionizable particles in the gaseous medium at leastpartially by comparing the value of the electrical property at the firstpoint in time to the electrical property at the second point in time.

The respirator sensor system 300 may be utilized to detect fluidionizable particles in a gaseous medium. The method includes contactinga gaseous medium with a fluid ionizable particulate matter sensingelement, and condensing a component of the gaseous medium on at least aportion of the fluid ionizable particulate matter sensing element; anddetermining an electrical property at a first frequency, such as 1 Hz,between a pair of electrodes of the fluid ionizable particulate matterdetection element; and determining an electrical property at a secondfrequency, such as 100 kHz, between a pair of electrodes of the fluidionizable particulate matter detection element; and determining a valuerelated to the presence of fluid ionizable particles in the gaseousmedium at least partially by comparing the value of the electricalproperty at the first frequency to the electrical property at the secondfrequency. The frequency may include DC.

The respirator sensor system 300 may include an additional computingsystem or remote device 350 wherein data is communicated between therespirator sensor system 300 and the additional computing system orremote device 350. In some embodiments, the additional computing systemis a cloud computing architecture. The communication between the reader330 and the additional computing system or remote device 350 may be viaa wired connection or via wireless internet network. The additionalcomputing system or remote device 350 may record data transmitted by thereader 330. The additional computing system or remote device 350 mayprocess data transmitted by the reader 330, and communicate informationback to the reader 330.

The respirator sensor system 300 may be utilized to detect fluidionizable particles in a gaseous medium. The method includes contactinga gaseous medium with a fluid ionizable particulate matter sensingelement, and condensing a component of the gaseous medium on at least aportion of the fluid ionizable particulate matter sensing element; anddetermining an electrical property between a first pair of electrodes ofthe fluid ionizable particulate matter detection element; anddetermining an electrical property between a second pair of electrodesof the fluid ionizable particulate matter detection element; anddetermining a value related to the presence of fluid ionizable particlesin the gaseous medium at least partially by comparing the value of theelectrical property of the first pair of electrodes to the electricalproperty of the second pair of electrodes.

The method may include the second pair of electrodes utilized as areference electrode. The reference electrode may be an analyte referenceelectrode. The reference electrode may be isolated from a targetcomponent of the gaseous medium. The target component of the gaseousmedium may be a fluid ionizable particle, such as a salt, for example.

The respirator sensor system 300 may be utilized to provide real-timefeedback on the quality of the respirator fit. The respirator sensorsystem 300 may be utilized to provide a method of fit testing. The fittesting method includes providing a respirator, then providing a sensorincluding a sensing element removably positioned substantially within aninterior gas space of the respirator, then providing a reader configuredto be in wireless communication with the sensor; and positioning therespirator over a mouth and a nose of a user while the sensor ispositioned substantially within an interior gas space of the respirator;and observing respirator fit assessment data communicated from thesensor to the reader.

The respirator sensor system 300 may be utilized with a computer visiontool or camera to assure a consistent quality of the respirator fit. Themethod includes: 1) The respirator wearer undergoes respirator fittesting while standing in front of a camera. The fit test is conductedwith the selected respirator model equipped with wireless aerosol sensordescribed herein. 2) The sensor measures aerosol leakage into therespirator in real time as the worker adjusts the respirator to fithis/her face. 3) Once the measured aerosol leakage drops below acceptedthreshold ensuring proper fit, the wireless sensor automatically signalsthe camera to capture the image of the respirator in its correct fitposition on the worker's face. 4) The captured image is analyzed andsaved to be used as reference in the future whenever the worker dons arespirator, to ensuring consistent respirator fit position on theworker's face. The image may be captured at any point during the test,such as before the test begins, to be subsequently linked to the fitvalue determined by the wireless aerosol sensor system.

The term “fit position” describes the configuration, position andorientation of the respirator on the user's face. Fit position includesposition of nose clip, shape of nose clip, position of straps,orientation on the face. An imaging sensor may include a traditional RGBsensor and may also include a NIR camera, depth sensor, and the like.

The worker may compare the “fit position” image with the currentplacement of the respirator on the worker's face. Adjustment to therespirator fit may be made until the “fit position” matches orsubstantially matches the current placement of the respirator on theworker's face.

Objects and advantages of this disclosure are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this disclosure.

EXAMPLES

All parts, percentages, ratios, etc. in the examples are by weight,unless noted otherwise. Solvents and other reagents used were obtainedfrom Sigma-Aldrich Corp., St. Louis, Mo. unless specified differently.

Sodium Chloride Aerosol Sensor

Sensor elements were constructed according to the method described inFIG. 5A and FIG. 5B and evaluated for respirator fit testingapplications.

The electrical impedance of a medium is a function of the number ofmobile charge carriers in the medium, the unit charge of the carriers,as well as their opposition to motion induced by coulombic forces. As aresult, the electrical impedance of a liquid solvent with a dissolvedionic solute is generally a function of the concentration of the solute.A sensing element, such as the one described above, may be used to probethe electrical impedance of a medium by contacting the electrodes withthe medium and monitoring the resistance to an applied electric field.In fluid media, such as water, the electric field is typically analternating field at a prescribed frequency which can provide bothresistive and reactive impedance information.

As an example, FIG. 11 shows the electrical impedance, specifically theimpedance magnitude, phase shift, resistance and reactance as a functionof frequency, of a sensing element such as the one described above whenimmersed in water/sodium chloride solutions of different concentrations.FIG. 11 top row are graphs illustrating the sensor response to differentconcentrations of NaCl in water, the resistance (solid lines) andreactance (dashed lines), as a function of frequency, measured by thesensor when coated with a liquid layer of the solution indicated.R=resistance, X=reactance. FIG. 11 bottom row are graphs illustratingthe sensor response to different concentrations of NaCl in water,corresponding impedance magnitude (solid lines) and phase shift (dashedlines), as a function of frequency, measured by the sensor when coatedwith a liquid layer of the solution indicated. Z=impedance magnitude,Theta=phase shift.

The impedance data is recorded by a Precision Impedance Analyzer 4294Aavailable from Agilent, USA. A significant decrease in the impedancemagnitude and resistance of the media (plotted on a log scale) is seenwith an increase in conductivity, as well as shifts in the overallprofile of all the curves. While this example is a case of a liquidmedia and not an aerosol, the underlying mechanism of the measurementforms the basis of how the sensors described in this application may beused to measure solution ionizable aerosols, as described below.

The compositions described thus far may be configured to alter theperformance of a fluid ionizable aerosol sensing element. Exemplary datathat illustrates the principal is shown in FIG. 12A-12C. FIG. 12A-12Care graphs that illustrate a comparison of isothermal water uptake andNaCl aerosol response for different surface modification and coatingsystems applied to a salt aerosol sensor.

The setup for the experiment used to generate the data in FIG. 12A-12Cis as follows: a fluid ionizable sensing element, with a pair ofinterdigitated conducting electrodes on the surface, is connected to anelectrical impedance spectrum analyzer. At t=0, the impedance spectrumrecording of the sensor begins. At t=60 s, the sensor is placed into atest chamber which is flowing air at 15 liters per minute, withapproximately 95% relative humidity. The sensing element is in fluidcontact with a portion of the flow. At the indicated time in each plot(‘NaCl aerosol on’), an aerosol containing approximately 10 μg/L NaClaerosol, with a mass mean particle diameter of 2 micrometers, isintroduced in the flow stream. The aerosol stream is generated byatomizing a NaCl/water solution of approximately 5 wt % NaCl using anatomizer. The aerosol stream is then removed at the indicated time(‘NaCl aerosol off’).

For the duration of the experiment, the sensing element is approximatelyin thermal equilibrium with the air stream, and the temperature of theairstream is constant. FIG. 12A shows the response of an exemplarysensing element with no surface modification to change the surfaceenergy, FIG. 12B shows that of a sensing element with theplasma+zwitterionic silane surface modification (described in FIG. 5A),and FIG. 12C that of a sensing element with the plasma+zwitterionicsilane surface modification with an additional glucose layer (asdescribed in FIG. 5B).

FIG. 12A illustrates the sensing element with no surface modification orcoating layer shows no significant change in electrical impedance at anypoint during the experiment.

This sensing element with no modification does not have a strongaffinity to form a fluid layer on the surface, and therefore lacks astrong mechanism in which the NaCl aerosol particles may ionize on thesensing element.

FIG. 12B illustrates that the sensing element with onlyplasma+zwitterionic silane treatment results in a small decrease inimpedance in response to humid air, and an additional decreasethroughout the duration of NaCl aerosol exposure. A small increase inimpedance once the aerosol stream is removed is likely due to a smallchange in humidity introduced by the NaCl aerosol stream.

This sensing element with only the plasma+zwitterionic silane treatmentenables a hydrophilic surface on the electrodes, which promotes someamount of fluid condensation, however at thermal equilibrium, thedriving force for fluid formation on the surface is lower than that ofthe sensing element with the additional hygroscopic material layer (FIG.12C).

FIG. 12C illustrates the sensing element with plasma+zwitterionic silanesurface treatment and also the glucose layer shows a much moresignificant response to the humid air stream, and then to the NaClaerosol stream. This is due to the hygroscopic property changes of thesensing element introduced by the addition of the glucose (hygroscopicmaterial) layer.

An example of how changing the coating weight of the hygroscopicmaterial layer may impact the sensing element response is shown in FIG.13A-13D, which illustrates the results of an experiment similar to thatof FIG. 12C, with variations in hygroscopic layer coating weight. FIG.13A-13D are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for O2+TMS plasma+zwitterionic silanefollowed by different coat weights of glucose applied to the saltaerosol sensor.

FIG. 14A-14C are graphs that illustrate a comparison of isothermal wateruptake and NaCl aerosol response for sensors with and without a filterelement. An example of how a particulate filter may be used to create areference electrode pair, as described in FIG. 7 and FIG. 8, is shown bythe data in FIG. 14A-14C.

All tests are conducted with the sensing element in the flow stream of ahumidity controlled NaCl aerosol system. The aerosol is generated byatomized a solution of 5 wt % NaCl in water using an atomizer. Thehumidity of all tests is between 95% RH and 100% RH. The sensing elementin all tests is an interdigitated array, with 5 mil line/space widths ofthe digits, with ˜0.5 cm² area. The graphs show the impedance magnitude(solid lines) and phase shift (dashed lines) over time at five differentfrequencies. The impedance data is recorded by a Precision ImpedanceAnalyzer 4294A available from Agilent, USA.

For example, FIG. 14A shows the response of a sensing element,substantially similar to those described in this application, with noparticulate filter, which is inserted into an airstream containingaerosolized sodium chloride microparticles and nanoparticles.

FIG. 14B shows a similar experiment, where the aerosolized solution doesnot contain sodium chloride, such that aerosolized solution producesonly water vapor without sodium chloride particles.

FIG. 14C shows the result of the same experiment as that in FIG. 14A,except that the sensing element is configured with a particulate filteras described previously. The similarities of the response shown in FIG.14B and FIG. 14C demonstrate that the particulate filter adequatelyallows the fluid components, such as water vapor, to contact thereference electrode pair, but prevents the particulate matter fromcontacting the reference electrode pair.

Thus, embodiments of SENSING ELEMENT FOR RESPIRATOR are disclosed.

All references and publications cited herein are expressly incorporatedherein by reference in their entirety into this disclosure, except tothe extent they may directly contradict this disclosure. Althoughspecific embodiments have been illustrated and described herein, it willbe appreciated by those of ordinary skill in the art that a variety ofalternate and/or equivalent implementations can be substituted for thespecific embodiments shown and described without departing from thescope of the present disclosure. This application is intended to coverany adaptations or variations of the specific embodiments discussedherein. Therefore, it is intended that this disclosure be limited onlyby the claims and the equivalents thereof. The disclosed embodiments arepresented for purposes of illustration and not limitation.

1. A respirator comprising a sensing element, wherein the sensingelements comprises: a substrate comprising an electricallynon-conductive surface; at least one high surface energy region; and anelectrode pair structure disposed on the electrically non-conductivesurface, the electrode pair structure comprises at least one pair ofelectrodes having a gap therebetween, and at least one of the electrodesis at least partially within the at least one high surface energyregion, and the sensing element is configured to sense fluid-solubleparticulate matter.
 2. The respirator of claim 1, further comprising twoor more pairs of electrodes.
 3. The respirator according to claim 1,wherein electrodes in the at least one pair of electrodes are positionedco-planar with respect to one another.
 4. The respirator according toclaim 1, wherein when the sensing element is configured to sensefluid-soluble particulate matter, a liquid layer is disposed in the gapsuch that the liquid layer is in contact with both electrodes in the atleast one pair of electrodes.
 5. The respirator according to claim 1,wherein the substrate further comprises at least one low surface energyregion.
 6. The respirator according to claim 1, further comprising afiltering element disposed around the surface of at least one electrode,such that a fluid must substantially pass through the filtering elementto reach the electrode.
 7. The respirator according claim 1, wherein theat least one high surface energy region comprises a siloxane surface. 8.The respirator according to claim 1, wherein the at least one highsurface energy region comprises a zwitterionic siloxane surface.
 9. Therespirator according to claim 1, wherein the at least one high surfaceenergy region comprises a hygroscopic material.
 10. The respiratoraccording to claim 1, wherein at least one of the high surface energyregions is fully circumscribed by a low surface energy region.
 11. Therespirator according to claim 1, wherein the water dissolvable ioncontent of the high surface energy regions is less than 1E-9 molesion/mm².
 12. The respirator according to claim 1, further comprising atleast one of a layer of hygroscopic material and a layer of a saltdisposed on the high surface energy regions.
 13. The respiratoraccording to claim 1, further comprising a layer of hygroscopic materialand a layer of salt disposed on the high surface energy regions.
 14. Therespirator according to claim 1, wherein the electrode pair structurecomprises four electrodes, A, B, C, and D, and two pairs of electrodesare formed, A-B and C-D.
 15. The respirator according to claim 1,wherein the electrode pair structure comprises three electrodes, A, Band C, further wherein two pairs of electrodes are formed, A-C and B-C,and electrode C is common to both electrode pairs.
 16. The respiratoraccording to claim 1, further comprising a protective film disposed onthe surface of the element.
 17. The respirator according to claim 6,wherein the filtering element is adhered to the surface by an adhesivefoam.
 18. The respirator of claim 16, wherein the foam has an ioncontent of less than 1000 ppm.
 19. The respirator according to claim 9,wherein the hygroscopic material is a polyol.
 20. The respiratoraccording to claim 19, wherein the polyol is a sugar alcohol. 21-22.(canceled)